docs: updates for agent_view release

[haleychaas]

Summary

This updates the documentation around the new agent_view and recommendations moving away from assistant_view, with links to the docs and changelog entry on that. I updated the code sample to match the sample app updates too.

Preview: https://docs-slack-d-branch-for-avumma.herokuapp.com/tools/bolt-js/concepts/adding-agent-features

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 9de76fb

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.48%. Comparing base (e3936b4) to head (9de76fb).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2995   +/-   ##
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  Coverage   94.48%   94.48%           
=======================================
  Files          45       45           
  Lines        7900     7900           
  Branches      708      708           
=======================================
  Hits         7464     7464           
  Misses        428      428           
  Partials        8        8           

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